Changing the color of keratinous fibers, in particular hair, represents an important area of modern cosmetics. The appearance of the hair may thus be adapted to current fashion trends and to the person's individual preferences. Various options are known to those skilled in the art for changing the color of the hair. The hair color may be temporarily changed by using direct dyes. In the process, dyes which are already formed diffuse from the coloring agent into the hair fiber. Although coloration using direct dyes involves little damage to the hair, it is disadvantageous that the colorings obtained with direct dyes are not very durable and wash out quickly.
If the user desires a long-lasting color result or a shade that is lighter than his/her original hair color, oxidative color-changing agents are customarily used. For long-lasting, intense colorations having appropriate fastness properties, so-called oxidation dyes are used. Such coloring agents customarily include oxidation dye precursors, so-called developer components and coupler components, which form the actual dyes with one another under the influence of oxidizing agents. Oxidation dyes are characterized by long-lasting color results.
Extensive prior art already exists with regard to oxidative coloring agents. Considerable testing has been conducted, in particular for optimizing the fastness properties of the colorings that are achievable with these agents.
However, despite the large number of optimization tests already carried out, there is still a need for improvement of the fastness properties of oxidatively dyed keratin fibers, in particular when they are colored in a shade of red. In particular the wash fastness and light fastness of shades of red, violet, and copper cannot yet be considered to be optimal.
It is therefore desirable to provide oxidative coloring agents for achieving shades of red, violet, and copper having improved wash fastness and improved light fastness.
The wash fastness of a color shade is understood to mean the change in color of the hair strands colored with this shade under the influence of multiple hair washings. This change in color may involve a shift of the color toward another hue, or also lightening of the coloring. Both changes in color are equally undesirable to the user. Color shades with good wash fastness experience little or no change in color, even after repeated hair washings. The hair washing may take place using a shampoo, a conditioning shampoo, or a conditioner.
The light fastness of a color shade is understood to mean the change in color of the hair strands dyed with this shade under the influence of sunlight (i.e., solar radiation or UV or UV/Vis radiation). Lightening of the dyed hair is generally observed upon exposure to sunlight. Shades having good light fastness experience little visible lightening of the color, even after multi-day exposure to sunlight.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with this background of the invention.